They live on opposite sides of the planet, but people in Malawi and Venezuela have similar microbes in their guts. Americans, on the other hand, have a distinctive microbiome with about 25 percent less diversity than indigenous Venezuelans’.

It comes down largely to diet, researchers determined after comparing more than 500 people from rural Malawi, the United States and the Guahibo society in Venezuela. Malawian and Guahibo diets are rich in corn and cassava, with meat an occasional treat. Gu...